Sufficient amounts of histidine decarboxylase from Lactobacillus 30a will be purified to permit accumulation of sufficient native enzyme to permit amino acid sequencing studies to begin on its two dissimilar subunits. Studies of the biogenesis of this enzyme from its proenzyme, and of its mechanism of action will be continued; these will include a determination of the effect of covalent modification on both catalytic activity and capacity of the two subunit to reassociate. Mechanistic studies of the synthesis of tryptophan from indole, pyruvate and ammonia by the tryptophanase from Escherichia coli will be emphasized; the mechanism of action of this enzyme will be compared with that of D-serine dehydratase, also from E. coli, which catalyzes a formally similar reaction although it is organized in quite a different way. Similar mechanistic studies of an oxygenase that cleaves the pyridine ring during the utilization of vitamin B6 as a sole source of carbon by a pseudomonad will be studied. The enzyme is unique among dioxygenases in the nature of the reaction it catalyzes. BIBLIOGRAPHIC REFERENCES: Mulligan, J.H., and Snell, E.E. Transport and metabolism of vitamin B6 in lactic acid bacteria. J. Biol. Chem. (1977) 252, 835-839. Suelter, C.H., and Snell, E.E. Monovalent cation activation of tryptophanase. J. Biol. Chem. (1977) 252, 1852-1857.